SUMMARY Transforming growth factor beta receptor type I/II (TRI/II) signaling is activated on the plasma membrane (PM) by ligand binding, inducing Smad3/4-dependent (canonical) or independent cell migration, invasion and/or metastasis. While Smad3/4 activates, Smad7 binds and inhibits TRI/II signaling. Primary cilia are protrusions of PM that mediate cell-to-cell communication and migration/invasion without affecting cell motility by activating various signaling pathways such as sonic hedgehog (Shh). Ceramide is a bioactive sphingolipid with tumor suppressive signaling functions, and ceramide synthase 4 (CerS4) generates long chain C18/20- ceramide. However, any mechanistic link between ceramide metabolism, Smad7 recruitment and TRI/II signaling at the primary cilium membrane for the regulation of tumor metastasis remains unknown. Based on our novel and unpublished preliminary data, we designed this application to test a novel hypothesis that CerS4/ceramide inhibits TRI/II trafficking and signaling selectively at the primary cilia membrane via Smad7 to modulate cell migration, invasion and/or metastasis. The following Specific Aims are proposed: Aim 1) Define the mechanisms by which ceramide regulates TRI/II signaling by Smad7; Aim 2) Determine the mechanisms by which ceramide/Smad7 inhibitory complex regulates TRI/II trafficking to the primary cilia; and Aim 3) Dissect the downstream mechanism by which TRI/II signaling at primary cilia induces tumor metastasis in response to alterations of the CerS4/ceramide/Smad7 axis. Overall, based on our expertise in cancer signaling and lipid metabolism, we are uniquely positioned to develop novel mechanism-based strategies for targeting/inhibiting TRI/II signaling selectively in primary cilium, which then will help attenuate tumor metastasis without affecting canonical functions of TGF- signaling (reducing general toxicity), using innovative molecular/pharmacologic tools, genetic models, and clinical specimens.